Electrolyte transport in rat colon: comparative effects of intestinal resections and bypass

In the present study the influence of different types of intestinal resection (50% distal and 50% proximal small bowel resection) and bypass (50% jejunoileal bypass) upon water and electrolyte (Na and K) colonic transport was examined. Four weeks after resections and bypasses no significant changes in wet and dry tissue weights, serum sodium and potassium values were found in comparison to sham-operated controls. In vivo net absorption of sodium, measured in micromoles of 22Na+ which disappeared from the medium during a determined period (15, 30, 45 and 60 min), in sham-operated animals, showed a gradual increase with the increase in the perfusion time, rising from 144 +/- 20 mumol at 15 min of perfusion to 425 +/- 28 mumol at 60 min. One month after the resection, Na absorption, expressed as total absorption and as micromoles per square centimeter, was not significantly modified in animals distally and proximally resected, but did significantly increase in bypassed rats with respect to sham-operated animals. When the results were calculated taking into account the tissue wet weight, the values of the resected rats continued to show no modifications; however, there was a compensation in the bypassed rats. These data demonstrate that the increase in the absorptive capacity of the colon in bypassed rats is due to morphological changes, which could originate from the trophic influence of enteroglucagon or from the effect of the secretions which flowed directly into the colon from the blind loop, an action which does not occur in resected rats. The effects of resection and bypass upon K+ colonic secretion showed no significant differences among the groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced excretion rates induced by small-scale turbulence in Acartia (Copepoda: Calanoida)

Several experiments have been performed on three congenericspecies of the calanoid copepod Acartia to determine the effectsof small-scale turbulence on metabolic rates. Both inorganicnitrogen and phosphorus excretion rates significantly increased     

Identification of guanine and adenine nucleotides as activators of glucose-1,6-bisphosphatase activity from rat skeletal muscle.

Glucose-1,6-bisphosphatase activity in rat skeletal muscle extracts was lost after exhaustive dialysis or precipitation with ammonium sulfate. Most of the original activity was recovered when the boiled extract was added to the ammonium sulfate precipitate. Qualitative analysis of the boiled extract revealed that the activator was either a nucleoside or a nucleotide. The results show that at concentrations between 0.05 and 1 mM, only guanine and adenosine derivatives are effective as activators, the former being more powerful. However, only guanosine, ADP, and AMP have an activating effect at the concentrations found in the boiled extract. The results of assays in vitro suggest that adenine nucleotides could be physiological modulators of glucose-1,6-bisphosphatase activity during muscle contraction.     

Adenosine deaminase affects ligand-induced signalling by interacting with cell surface adenosine receptors

Adenosine deaminase (ADA) is not only a cytosolic enzyme but can be found as an ecto-enzyme. At the plasma membrane, an adenosine deaminase binding protein (CD26, also known as dipeptidylpeptidase IV) has been identified but the functional role of this ADA/CD26 complex is unclear. Here by confocal microscopy, affinity chromatography and coprecipitation experiments we show that A₁ adenosine receptor (A₁R) is a second ecto-ADA binding protein. Binding of ADA to A₁R increased its affinity for the ligand thus suggesting that ADA was needed for an effective coupling between A₁R and heterotrimeric G proteins. This was confirmed by the fact that ASA, independently of its catalytic behaviour, enhanced the ligand-induced second messenger production via A₁R. These findings demonstrate that, apart from the cleavage of adenosine, a further role of ecto-adenosine deaminase on the cell surface is to facilitate the signal transduction via A₁R.     

Enolase Activity and Isoenzyme Distribution in Human Brain Regions and Tumors

Abstract: The distribution of enolase (EC 4.2.1.11) activity and isoenzymes in various regions of human brain at different ages (from 23 weeks of gestation to 95 years) and in brain tumors has been determined. Total enolase activity increased in all regions with age. No significant differences were found in the relative proportions of αα-, αγ-, and γγ-enolase isoenzymes in the various brain regions, determined by agarose gel electrophoresis. Type αα-enolase was the predominant isoenzyme, and αγ-enolase represented a substantial proportion of the total enolase activity. Astrocytomas, anaplastic astrocytomas, glioblastomas, and meningiomas possessed lower enolase activity than normal brain. Among astrocytic tumors, total enolase activity correlated with malignancy. Astrocytomas possessed the lowest and glioblastomas the highest enolase activity. All tumors possessed a higher proportion of αα-enolase and a lower proportion of γγ-enolase than the normal human brain. Among astrocytic tumors, glioblastomas were the tumors with the highest proportion of αα-enolase and lowest proportion of γγ-enolase.     

Nitric oxide synthase inhibitors decrease human polymorphonuclear leukocyte luminol-dependent chemiluminescence

Nitric oxide synthase (NOS) inhibitors have been reported to modulate luminol-dependent chemiluminescence (CL) in rat macrophages, whereas the potent oxidant peroxynitrite (ONOO^-) was shown to react with luminol to yield CL in a cellfree system. We evaluated the role of the -arginine/NOS pathway in luminol CL by phorbol ester-activated human polymorpho-nuclear (PMN) leukocytes using the NOS inhibitors N^G-monomethyl- -arginine ( -NMMA) and N-iminoethyl- -omithine ( -NIO). Nitric oxide (·NO) release was determined by oxidation of oxymyoglobin. In addition, the effect of NOS inhibitors on superoxide anion O₂^-) production was measured. Luminol CL was notably diminished by -NMMA in a dose-dependent manner. Superoxide dismutase (SOD) also decreased luminol CL and -NMMA potentiated light emission decrease produced by SOD. Nitric oxide and O₂^·- production was significantly decreased by -NMMA; moreover, luminol-dependent CL but not O₂^·- production was attenuated by -NIO. These data suggest that products of catalytic activity of both ·NO synthase and NADPH oxidase are required to elicit maximal luminol CL in this system. These studies demonstrate that the NOS synthase pathway is involved in luminol CL by human PMN, and they suggest that ONOO would be an unrecognized mediator in this phenomenon.     

A model of the pentose phosphate pathway in rat liver cells

A mathematical model based on kinetic data taken from the literature is presented for the pentose phosphate pathway in fasted rat liver steady-state. Since the oxidative and non oxidative pentose phosphate pathway can act independently, the complete (oxidative + non oxidative) and the non oxidative pentose pathway were simulated.Sensitivity analyses are reported which show that the fluxes are mainly regulated by D-glucose-6-phosphate dehydrogenase (for the oxidative pathway) and by transketolase (for the non oxidative pathway). The most influent metabolites were the group ATP, ADP, P₁ and the group NADPH, NADP⁺ (for the non oxidative pathway).Abbreviations GK Glucokinase, (E.C. 2.7.1.2.) - G6PDH D-glucose-6-phosphate dehydrogenase, (E.C. 1.1.1.49) - PLase 6-Phosphogluconelactonase, (E.C. 3.1.1.31.) - PGIcDH 6-Phosphogluconate dehydrogenase, (E.C. 1.1.1.44) - RPI D-ribose-5-phosphate keto-isomerase, (E.C. 5.3.1.6) - TK D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate glycol-aldehyde transferase, (E.C. 2.2.1.1.) - TA D-sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate dihydroxyacetone transferase, (E.C. 2.2.1.2) - EP D-ribulose-5-phosphate-3-epimerase, (E.C. 5.1.3.1) - PGI D-glucose-6-phosphate keto-isomerase, (E.C. 5.3.1.9) - TPI D-glyceraldehyde-3-phosphate keto-isomerase, (E.C.5.3.1.1)     

The effect of bedrock type,temperature and moisture on species richness of Pyrenean Scots pine (Pinus sylvestris L.) forests

The relationship between environmental parameters (bedrock type, temperature and moisture index) and understorey species richness was studied from a large phytosociological data base on Pyrenean Scots pine (Pinus sylvestris L.) forests. Generalized linear models were used to test this relationship. Total species richness and species richness of the different life forms were considered. The results suggest different patterns for the different life forms, and that the richest forest was on the calcareous bedrock of north-facing slopes at low altitudes.